This invention relates to electronic components such as semiconductor devices.
Recently, in response to the demand for compact and light electronic appliances, there is a strong trend of miniaturizing electronic components incorporated in electronic appliances. Generally, electronic components are mounted on a printed circuit board disposed within an electronic appliance. More lately, in particular, in order to increase the mounting density of electronic components on the printed circuit board, the electronic components are often affixed to both sides of the printed circuit board by soldering, or so-called surface mounting is widely employed.
Incidentally, a semiconductor device is one of such electronic components usually encapsulated in a resin package. Often used as the package of the semiconductor device to be surface mounted on a printed circuit board is the small-outline "J" lead package (referred to as SOJ package hereinafter).
In FIGS. 2(A), (B), a semiconductor device encapsulated in a conventional SOJ package is shown.
In the figures, a semiconductor chip (not shown) is encapsulated in a resin package 1 having a substantially rectangular parallelepiped shape. At the lower surface of the package 1, nearly semicircular protrusions 2 extend along the sides thereof. A part of a lead frame electrically connected to the semiconductor chip projects from both sides of the package 1 as plural external leads 7. Each external lead 7 is bent to a J-shape to cover the protrusions 2 by conforming to the contour of the protrusions 2 of the package.
When mounting a semiconductor device encapsulated within a thus composed SOJ package on a printed circuit board, as shown in FIG. 2(B), each external lead 7 is positioned on the wiring pattern 5 of the printed circuit board 4, and the semiconductor device is temporarily fixed on the surface of the printed circuit board 4. Afterwards, by employing the so-called dip method of passing the printed circuit board 4 through a solder bath, or by employing the so-called reflow method of heating and melting the solder by infrared rays, the solder 6 is melted, and the external leads 7 are connected to the wiring pattern 5 of the printed circuit board 4.
Thus, in the SOJ package, since the external leads 7 are formed in a state tightly contacting with side and lower surfaces of the package 1, when the semiconductor device is mounted on the printed circuit board 4, the space occupied by the semiconductor device is minimized in both the vertical and the lateral directions, so that a high mounting density may be realized.
The semiconductor device encapsulated in the SOJ package is mounted on both sides of the printed circuit board together with other small electronic components. However, the semiconductor chip may be broken in the course of long use or due to some other cause. In such a case, the semiconductor device must be replaced with a normal one. In the SOJ package, however, the soldered parts are located beneath the package 1. Still further, various electronic components are densely mounted on both sides of the printed circuit board. It is accordingly extremely difficult to simultaneously melt the solder of the multiple external leads of the defective semiconductor device to detach the semiconductor device from the printed circuit board. If it is attempted to remove the semiconductor device from the printed circuit board by force, the adjacent electronic components may be broken. Furthermore, even if the defective semiconductor device can be dismounted from the printed circuit board, it is next to impossible to solder a normal semiconductor device in its place.
Therefore, hitherto, if the semiconductor device in the SOJ package became defective, it was required to replace the expensive printed circuit board having multiple electronic components assembled thereto in order to repair the electronic appliance.